Transverse electromagnetic devices for ferrite loaded planar circuits

ABSTRACT

DESCRIBED IS AN INTERGITITAL WAVE CIRCUIT DEPOSITED ON A FERRITE FILM AND HAVING A DIRECT CURRENT MAGNETIC FIELD APPLIED IN THE PLANE OF THE INTERDIGITAL CIRCUIT TO PROVIDE A MICROWAVE DEVICE EMPLOYING GYROMAGNETIC MEDIA FOR PHASE SHIFT, FREQUENCY TRANSLATION, CIRCULATION AND THE LIKE.

' Filed Feb. 26, 1969 Jan. 5,1971 c, BUCK 3,553,733

' TRANSVERSE ELECTROMAGNETIC DEVICES FOR FERRITE LOADED PLANAR CIRCUITS2 Sheets-Sheet 1 PHASE SHIFT Fig. 2

INVENTOR,

DANIEL C. BUCK ATTORNEY Jan- 5, 1971 D. c. BUCK 3,553,733

TRANSVERSE ELECTROMAGNETIC DEVICES FOR FERRITE LOADED PLANAR CIRCUITSFiled Feb. 26, 1969 2 Sheets-Sheet 2 INVENTOR.

DANIEL C. BUCK Fig.5

Arromvzr United States Patent US. Cl. 343854 8 Claims ABSTRACT OF THEDISCLOSURE Described is an interdigital wave circuit deposited on aferrite film and having a direct current magnetic field applied in theplane of the interdigital circuit to provide a microwave deviceemploying gyromagnetic media for phase shift, frequency translation,circulation and the like.

Ferrite phase shifters are now well known and usually comprise a slab orrod of ferrite material disposed in a wave guide, together with anexternal permanent magnet or electromagnet which produces lines of fluxwhich pass through the walls of the wave guide and the ferrite bodyitself. By varying the strength of the magnetic field, the phase shiftcaused by the ferrite slab can be varied.

Wave guide systems and conventional ferrite phase shifters, however, aresomewhat bulky, particularly in applications such as electronicallyscanned fixed antenna systems employing a plurality of radiatingelements whose phases are electronically varied. That is, by varying thephases of the respective signals fed to the individual radiatingelements, the composite radiated beam can be caused to scan back andforth without mechanical movement of the antenna itself. Due to thespacing between and weigh too much in the case of airborne antennas.

In an effort to reduce the size of Wave transmission lines, microstripplanar devices have been developed which comprise an insulatingdielectric slab sandwiched between a metallic strip conductor and aground plate. Efforts have been made to provide microstrip ferrite phaseshifters for such devices wherein a ferrite film is deposited on asubstrate, and the substrate with the ferrite film positioned betweenthe upper and lower conductors of the microstrip planar transmissionline. Unfortunately, mechanically deposited ferrite films are mosteasily deposited on ceramic substrates. This is a disadvantage inmicrostrip planar miniaturized devices since the ceramic substrateoccupies most of the space between the ground plane and the periodicwave circuit. This reduces the available phase shift substantially inproportion to the amount of dielectric in the microstrip circuit.

SUMMARY OF THE INVENTION As an overall object, the present inventionseeks to provide a planar transverse electromagnetic circuit which canbe used for both reciprocal and non-reciprocal devices and which has theproperty of having both conductors in a common plane. In this manner,the device becomes extremely compact.

Another object of the invention is to provide a planar interdigital wavecircuit on a ferrite film, deposited on an insulating substrate, andhaving a direct current magnetic field applied in a directionsubstantially parallel to that of the digits.

In accordance with the invention, a phase shift device forelectromagnetic wave energy is provided comprising a ferrite filmdeposited on an insulating substrate, strip conductors deposited on theferrite film and forming an interdigital circuit, and means for inducinglines of magnetic flux in the ferrite film to thereby vary the phase ofmicrowave energy passing through the interdigital circuit.

Preferably, the insulating substrate comprises a ceramic, while theelectrical conductors are deposited on the ferrite in a photoresistetching technique similar to that used in the manufacture of printedcircuits. Each interdigital circuit comprises a pair of parallelconductors having conductors at right angles thereto which project intothe space between the parallel conductors alternately from one parallelconductor and then the other to provide a serpentine path for waveenergy passing through the device. By applying a magnetic field t0 theferrite film along the length of the interdigital circuit, and byvarying the magnitude of this magnetic field, variable phase shift ofmicrowave energy passing through the device can be achieved.

In one embodiment of the invention shown herein, interdigital linesformed on a ferrite film are fed in balanced pairs from coaxial lines.Each interdigital line can then be used as an array type phase shifterelement; and each coaxial line can drive two antenna elements and,therefore, act as a two-fold power splitter.

The above and other objects and features of the invention will becomeapparent from the following detailed description taken in connectionwith the accompanying drawings which form a part of this specification,and in which:

FIG. 1 is an isometric view of the phase shifting device of theinvention;

FIG. 2 is a graph of insertion phase versus frequency for the circuit ofFIG. 1;

FIGS. 3 and 4 illustrate a typical application of the phase shiftcircuit of the invention;

FIG. 5 shows the manner in which wave energy passes through the circuitof FIG. 3; and

FIG. 6 is an illustration of a plurality of phase shifters in a stackedarray.

With reference'now to the drawings, and particularly to FIG. 1, thephase shift device shown comprises a sub strate 10, preferably formedfrom ceramic material and having a film or layer of ferrite material 12deposited thereon. The film 12 is formed by depositing a mixture ofnitrates of iron and other metals, such as magnesium or magnesiumferrites, in an alcohol solution on the substrate 10. The deposit isthen air dried at several hundred degrees centigrade to boil out theorganics. It is then fired in a carefully controlled, moderatelyoxidizing atmosphere to a temperature above about 900 C., and thencooled in an inert atmosphere. After the ferrite film- 12 is formed onthe substrate 10, an interdigital circuit can be formed on the ferritefilm by conventional photoresist etch techniques wherein the entire film12 is covered with a copper film and then all but the desired circuitconfiguration etched away.

The interdigital circuit shown in FIG. 1 includes side strips orconductors 14 and 16 extending along the length of ferrite strip 12.Projecting outwardly into the space between the conductors 14 and 16 arestrips 18-26 of c'onducting material. The strips 18, 22 and 26, forexample, are connected to the side strip 16 but not to the strip 14.Alternate ones of the strips 20 and 24, in turn, are connected to theside strip 14 but not the strip 16. In this manner, a serpentine pathfor wave energy is provided wherein the electric vectors are parallel tothe ferrite strip 12 while the magnetic vectors are at right angles tothe strip. In this manner, a magnetic field applied parallel to theferrite strip 12 (i.e., along the digits formed by strips 1826) can beused to effect a shift in the insertion phase of an electromagnetic wavepassing through the interdigital circuit.

The dispersion properties of the circuit shown in FIG. 1 can be derivedfrom its Brillouin diagram shown in FIG. 2 which plots frequency versusphase shift per section or digit, P, of the interdigital line. Analysisshows that in the frequency range near w the magnetic field of theapplied electromagnetic wave is linearly polarized in the XY plane.Thus, an applied direct current field in the Z direction will causephase shift. For frequencies near W the magnetic field will have a largecircularly polarized component in the YZ plane. This requires that thedirect current field be in the X direction. Thus, one can build eitherreciprocal or non-reciprocal devices based on the interdigital line. Aswill be understood, there are upper and lower limiting frequencies foran interdigital circuit of given dimensions. Above or below theselimits, the circuit itself will radiate energy.

One such device is shown in FIGS. 3 and 4 where eight dipole antennas orradiating elements 28 are fed by four coaxial transmission lines 30, 32,34 and 36. Each coaxial transmission line comprises an inner centerconductor 38 surrounded by an outer metallic cylindrical shell 40.

At the terminating ends of the coaxial transmission lines 3036 is aferrite film 42 formed on a ceramic substrate 44 in the same manner asdescribed in connection with FIG. 1. Taking the coaxial transmissionline 36, for example, its center conductor 38 is connected to alongitudinal strip conductor 46, while the outer metallic shell 40 isconnected to longitudinal conducting strips 48 and 50 at points spaced180 apart. With this arrangement, two interdigital circuits are formed,one between the conductors 46 and 50 and the other between conductors 46and 48; the power from the coaxial line 36 being split between the twointerdigital circuits. Furthermore, by providing a toroid 52 for eachinterdigital circuit shown in FIG. 4 and by energizing anelectromagnetic coil 54 surrounding the toroid, a magnetic field will begenerated in the ferrite in the area of a specific interdigital circuit(i.e., that between strip conductors 46 and 50) to vary the phase of thewave energy passing through that particular interdigital circuit. Inthis manner, it will be readily appreciated that the direction ofpropagation of the wave front from the radiating elements 28 can be madeto scan to the left or right electronically.

The operation of the device of FIGS. 3 and 4 can perhaps best beunderstood by reference to FIG. 5. Within the coaxial transmission line,the electric vectors of the electromagnetic wave energy are radial;while the magnetic vectors, H, extend circumferentially around thecenter conductor 38. The wave fronts of the energy passing through thetwo interdigital circuits are indicated by the reference numerals and22. The electric vector E are now parallel to the ferrite film while themagnetic vectors are, of course, at right angles thereto. Note that thetwo wave fronts are 180 out of phase with respect to each other. Byapplying an external magnetic field, H or H along the length of theferrite strip, the phase of the electromagnetic wave energy can also bemade to vary.

Instead of using an external magnetic field as illustrated in FIG. 4,for example, it is also possible in accordance with the invention toutilize a film of latchable ferrite material and to pass conductorsthrough holes in the film. By reversing the flow of current through theconductors, various phase shift effects can be obtained.

Furthermore, it is possible to stack a plurality of interdigitalcircuits as shown, for example, in FIG. 6 where two phase shifters 60and 62 are stacked one above the other. Each phase shifter is connectedto a plurality of 4 dipole antennas 64 or 66 and fed from coaxialtransmission lines 68 or 70. The magnetic flux producing devices are, ofcourse, not shown in FIG. 6.

Although the invention has been shown in connection with certainspecific embodiments, it will be readily apparent to those skilled inthe art that various changes in form and arrangement of parts may bemade to suit requirements without departing from the spirit and scope ofthe invention.

I claim as my invention:

1. A planar circuit transverse electromagnetic ferrite device forelectromagnetic wave transmission systems, comprising a ferrite filmdeposited on a substrate, electrical strip conductors disposed on saidferrite film and forming an interdigital circuit, means for feeding waveenergy to one end of said interdigital circuit, and means for inducinglines of magnetic flux in said ferrite film to thereby vary thecharacteristics of wave energy pushing through the interdigital circuit.

2. The ferrite device of claim 1 wherein said substrate comprises aceramic material.

3. The ferrite device of claim 1 wherein said magnetic lines of flux areinduced in said film in a direction extending along the digits of saidinterdigital circuit.

4. The ferrite device of claim 1 wherein said interdigital circuitcomprises a pair of parallel conductors deposited along the length ofsaid ferrite film together with stub conductors at right angles to saidparallel conductors, said stub conductors being connected alternately toone and then the other of said parallel conductors to provide aserpentine path for wave energy passing through the interdigitalcircuit.

5. The ferrite device of claim 4 wherein at least two interdigitalcircuits are deposited on said ferrite film with a common centerconductor forming one of the two parallel conductors for eachinterdigital circuit.

6. The ferrite device of claim 5 wherein the means for feeding waveenergy to one end of each of the two interdigital circuits comprises acoaxial transmission line having its center conductor connected to saidcommon center conductor and its surrounding shell connected to theremaining two parallel conductors at points spaced about apart aroundsaid outer shell.

7. The ferrite device of claim 6 wherein the ends of said parallelconductors opposite said coaxial transmission line are connected todipole antennas.

8. The device of claim 7 wherein there are two substrates stacked oneabove the other, each of said substrates having ferrite films andinterdigital circuits deposited thereon, dipole antennas connected toone end of each of the conductors of the stacked interdigital circuits,and coaxial transmission lines connected to opposite ends of theparallel conductors of the stacked interdigital circuits.

References Cited UNITED STATES PATENTS 3,418,605 12/1968 Hair et al333-24.1 3,448,409 6/1969 Moose et al 333-84X 3,448,410 6/1969 Parks33331 ELI LIEBERMAN, Primary Examiner M. NUSSBAUM, Assistant ExaminerU.S. Cl. X.R. 33324.l, 31, 73

